Low-capacity vapor-electric device



June 17, 1952 J. L.. BOYER 2,600,390

LOW-CAPACITY VAPOR-ELECTRIC DEVICE Filed Dec. 20, 1950 Fig.|.

lNvENToR John L Boyer.

ATTORNEY Patented June 17, 1952 nLOW-('JAPACI'IJY VAPOR-ELECTRIC DEVICEJohn L. Boyer, Pittsburgh, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation oflennsylvaniaApplication December 20, 1950, Serial No.`201,783

Claims. 1

My invention relates to vapor-electric devices or tubes, andparticularlyto low-arc-drop hotcathode arc-discharge devices using aVaporizable discharge-metal selected from the group consisting ofcesium, rubidium and potassium. Such of temperatures on both the anodeand the cathode, thus making it diicult to have an economical design forsmall tubes of this class.

An object of my present invention is to providel "l l5 tubes have to beoperated with a narrow range a tube of the stated class, which does notrequire any complicated temperature-control. In the accomplishment ofthis object, I provide, among other things, a cooling-means whichincludes a fusible material having a melting-point at approximately thedesired temperature to which said cooling-means is to hold itsassociated internal portion of the device.

My invention is an improvement over a vaporelectric device which isdescribed and claimed in a copending application of August P. Colaiacoand myself, Serial No. 144,354, led February 15, 1950. As pointed out inthis copending application, the three metals, cesium, rubidium andpotassium, form a more or less distinctive class by themselves, whichmay be described as the alkali metals having four, five and six shellsin their atomic structure, or the stable alkali metals having more thanthree shells. The entire group of alkali metals consists of sixelements, of which the rst two and the last are readily distinguishablefrom the other three, with which my invention is particularly concerned.

The two lightest alkali metals, lithium (Li) and sodium (Na) areseparated, in some periodic tables, from the heavier light metals ofthealkali-metal group (IA), as being distinctive because of theirelectron-grouping. The physical and chemical characteristics of thesetwo lightest alkali-metals are also distinctively different from thegroup comprising cesium, rubidium and potassium. Sodium has a minimumbreakdown voltage which comes at too low a pressure-distance product pdfor my purposes; and it is also too active, chemically.. Lithium has avapor-pressure which is much too low for my purposes, as this lowvapor-pressure requires too high a temperature to obtain a practicallyusable Vvapor-pressure which is high enough to give a su'iciently highcurrent-density to be practical for my purposes.

The sixth and heaviest alkali metal, No. 87 in the periodic table, wasformerly called virginium, but has now been proved to be an elementwhich is called francium (Fa), an unstable 2. atomic-pile product whichis very radio-active, and which has an extremely short half-life of onlya few minutes, so that is is unsuitable for my purposes. W

It is also an object of my invention to provide a new tube-design inwhich the Ycesium or other i discharge-metal is condensed on the coldend of the cathode, as distinguished from being condensed elsewhere, ason the anode, as in certain previous designs. This condensation-place ofthe discharge-metal is determined by making the cold end of the cathodethe coolest partof the tube. This has the double advantage of gettingthe discharge-metal pool at the cathode-potential, in a place whichmakesit impossiblekto have positive-ion bombardment during the inversevoltage-periods, thus guarding against electronemission from this pooland consequent arcbacks during said inverse voltage-periods. Thedischarge-metal pool, at the cold end of the cathode, is also at a spotat which the temperature is not materially affected by the intensity ofthe arc, and hence not materially affected by the load-current, as 'inprevious tube-designs in which the discharge-metal pool was at or near apart of the anode.

My invention consists in the combinations,

systems, structures, parts, and methods of de- Y The form of embodiment`of my invention, as

shown in Fig. 1,Ycomp`rises an evacuatedV enclosure-meansincluding ananode-portion 5 of the enclosure-means', a Ycathode-portion 6 of theenclosure-means, and an insulator-to-rnetal sealing-means s between saidanoderand cathode portions. There is also enclosed, within the'enclosure-means, a quantity of a discharge-metal selected from thegroup comprising cesium, rubidium and potassium.

The cathode-portion 6 of the-enclosure-means includes a re-entrant metaltube-portion i6, whichextends into the enclosure-means. Thiscathode-tube I6 has aclosed inner end l1. .'The

inner endof the cathode-tube lcarriesperipheral metal fins I8, extendingcut radially therefrom, like a plurality of washers, for providing anextended cathode-surface which constitutes the active arc-terminatingsurface of the cathode.

The cathode-tube l and its fins iB are preferably made of nickel, oratleast the exposed surfaces of these parts, which are exposed to thevapors within the device, are preferably made of nickel. The rest of thecathode-portion E, and all of the anode-portion 5, may be made of eitheriron (including steel) or nickel.

The active part of the cathode, namely the cathode-tube portion carryingthe ns t8, has to be heated to a suitable emitting-temperature duringthe operation of the device. When cesium is the discharge-metal, thiscathode emittingtemperature is around '700 C. or '750 C., or evensomewhat higher; when rubidium is at the emitting-temperature, theactive cathode-portion should be maintained at a temperature of about700 or 720 C. to say 800 C.; and when potassium is the discharge-metal,the active cathode-temperature should be perhaps about 800 C'. to 900 C.

To heat the active emitting-surface of the cathode, I provide a,cathode-heater IS, which is disposed within the cathode-tube l5, theheater being preferably concentrated at the finned end of thecathode-tube, and being supplied with a sufficient amount of electricalenergy to maintain the desired temperature. The heater I9 may besupplied with electrical heating-energy through a terminal-lead 20 whichextends through an insulating seal 2l in the base 22 of thecathodeportion 6.

In vapor-electric devices of the class described, it is necessary tomaintain some internal portion of the device at a temperature which iscooler than any other internal portion of the device during theoperation of the device, so as to provide a condensation-surface onwhich Vapor of the discharge-metal condenses. The temperature of thiscondensation-surface determines the operating vapor-pressure of thedischarge-metal, and hence it is necessary to provide acondensation-temperature which is Within certain suitabletemperature-ranges, being about 220 C. for cesium, 240 C. for rubidium,or 280 C. for potassium, these temperatures being merely illustrative.All other internal portions, both metals and insulators, of the device(other than said condensation-surface) have to be maintained attemperatures which are higher than the condensation-temperature, inorder to prevent unwanted condensation.

In vapor-electric devices of the described class, it is also necessaryto variably cool the anode. The play of the arc on the anode tends toheat the anode to temperatures which, is unchecked, would be hot enoughto make the anode emit like a cathode, thus spoiling the operativenessof the tube. This anode-heating is a variable quantity, depending uponthe intensity of the arc, and hence upon the amount of loadcurrent whichis being carried by the vapor-electric device. It is usually desirableto keep the anode at a fairly uniform low temperature, in order to keepwell under the electron-emitting or backfiring-temperature of the anode.

In those discharge-tubes in which the condensation-surface is the anode,or a part of the anode. as will be described in connection with Fig. 3,the anode-temperature may be the condensation-temperature. In thosetypes of tube in which the condensation-surface is provided at some partof the tube other than the anode, as Will be described in connectionwith Fig. l, it is necessary to hold the anode to some temperature whichis higher than the condensation-temperature. When cesium is thedischarge-metal, for example, in Fig. 1, the anode-temperature mfy be232D C., or somewhere between 230 and 30 C.

In Fig. 1, I show a preferred form of embodiment of my device, in whicha non-linear coolingmeans is provided for the anode-portion 5, forautomatically providing approximately the amount of cooling which isnecessary to hold the anode at a fairly steady temperature. Thisnon-linear anode-cooling means, for the tube which is shown in Figs. 1and 2, is characterized by having a fusible material 25, which has amelting-point at approximately the desired temperature to which saidcooling-means holds its associated internal portion of the device, inthis case the anode-portion 5. When no portion of the anode-surface isthe condensation-surface, as in the tube illustrated in Fig. l, and whencesium is the discharge-metal, the fusible material 25 may be tin, whichmelts at 232 C., or it may be some metal alloy, or even an insulatingcompound, which has a melting-point between, say 230 and 300 C.

In the preferred form of construction of the fusible-materialcooling-means, provision is made for the natural thermally inducedcirculation of the fusible material 25 after it has melted. To this end,I preferably design the device so that the heat-radiatingenclosure-portion of the device, which is to be cooled, stands uprightor in a vertical position, as is the case of the tubular side-walls ofthe anode-portion 5 of the device. Spaeed from the outer surface of thisheat-radiating enclosure-portion (such as the tubular anode-surface 5) Iprovide an upstanding heat-barrier 30, which is suitable heat-insulatingsolid. When the heat-radiating enclosure-portion, such as 5, is tubularor cylindrical, the heat-barrier 30 is also tubular or cylindrical,

, being mounted on suitable pins or feet 3i.

Spaced from the other side of the heat-barrier 30, I provide anupstanding heat-radiating cooling-plate 35, which, if the heat-barrieris cylindrical, would also be cylindrical. The heatradiatingcooling-plate 35 radiates or conducts heat directly to the ambientatmosphere, either wth or Without the aid of heat-radiating fins 3 Thespace between the heat-radiating enclosure-portion, such as theanode-portion 5, and the cooling-plate 35, is lled with the fusiblematerial 25. For holding the fusible material 25 when it is melted, Iprovide a suitable container-means, such as is provided by top andbottom flanges 31 and 38 of the cooling-plate 35. The top and bottomends of the heat-barrier 30 are spaced from the top and bottom portions37 and 38 of this container-means, so that the molten fusible material25 can circulate over the top of the heat-barrier 30 and under thebottom of the heat-barrier; or other suitable disposition andarrangement of the barrier is made so that such a circulation will bepossible.

In the operation of the fusible-material cooling-means just described,the presence of the heat-barrier 30 prevents the conduction or radiationof very much heat from the anode-portion 5 of the evacuated container,as long as the fusible material 25 remains in its solid state, in whichit does not circulate. As soon as the egeooct anode-surface reaches?vthe I melting-point of the fusblematerial (T, however, the anode beginsto'inelt the `fusi/ble material, and the latent heat of vfusion ofthefusible material holds the anode to substantially the melting-point ofthis material', until substantially all of the fusible material ismelted. When this happens, the fusible material begins to circulate,with a naturalcirface of the anode 5 tothe inner surface of thecocling-plate may be assisted, if desirable, by providing heat-transferfins di) on the outer Sur- Y face of the anode 5, and otherheat-transfer ns I on the inner surface of the cooling-plate 35.

YIn the preferred illustrative form 0f construction of a vapor-electricdevice, as shown in Fig.

l,VIV I preferably make use of a special cathodeconstruction in whichthev active emitting inner end of the Cathode-tube I6 isheated'` (by theheater I9), and in which suitable means are provided for'externallycooling the outer, or enclosure-entering, end of the cathode-tube I6.The cathode-tube I8 is made long enough (and the tube-Walls are thinenough) so that the bottom end, or enclosure-entering end, of thiscathode-tube i6, or of the attached external cathode-parts, is thecoolest part of the device,

whereby the `discharge metal condenses thereon. Usually, as illustrated,the natural heatradiation from the exposed cathode-surfaces vMi Vto theambient atmosphere, without any coolingi'lns or external blowing-means,suices to keep the attached end of the cathode-tube I6 at a uniformtemperature which is just about right. Sometimes, it may be necessary toadd a certain amount of heat-insulation d?, for keeping thecathode-portion E of the evacuated container from getting too cool, andthis heat-insulation may be thickened, as indicated at lid, at placesWhere the internal tube-parts are to be kept at still hotter, ornon-condensation, temperatures, as in the vicinity ofthe insulator-partS.

It will thus be observed that I have provided, in Fig, 1, a basic designin which the dischargemetal condenses on a surface which is. not subjectto variable amounts of heating in response 'to variable load-currentscarried by the device.

rIhe cool bottom or outer endofthe cathodetube I6V is admirably suitedfor this purpose,

because the hot inner end of this cathode ltube necessarily operates ata fairlyconstant emittingtemperature, vand the cool bottom or outer .endof this tube is sulciently farremovedfrom vthe arcrso that itis notmaterially affected bythe intensity of the arc, which is anothervvay ofsaying that it is not materially affected bythe amount of load-currentWhich is being carried by the device. Inl a small, inexpensive`dischargetube, therefore, Without complicated automatictemperature-controlling means, it iseasy, .to d esign the tube so thatthe cool end of the,` cathodetube I6 operates at a fairly constanttemperature, independent of load-conditions. Y In Fig. 1, I have chosenthis cool-endYcathode;-temperature fasY the coolest temperature of thedevi c e or "the temperature at which condensation takes place, and atWhich the vapor-pressurefwithi the hdeviceis controlled. f f A Sincevthis coolingl or condensing-place for the alkali-metal pool (whichmaybe only a-few drops) is at the cold-end@ofthev cathode;v thisalkali-metal pool isat the cathode-potential, and henceY it -cannot haveany positive-ion-bombardment Which-if it were present, would initiateelectron-emission and cause faults during the tube-operation.. Thecollection Yof the alkalimetal-pool at the cold end of the cathode isfurther advantageous over previous vconstrui'ztions in which this poolvhas been collected at or near the `lower end of the anode of thedevice, because the lower end of the cathode is inherently much thebetter place, since its temperature `is not aiectedby the intensity 'of'the varc, and hence it is notaf'fected bythe load-current of thedevice. l f

In accordance with the preferred form of embodiment of` my invention, asshown in Fig. 1,

VI combine, withv this cathode-tube construction having the.condensation-surface `at itsV lower or outer end, a fusible-materialcooling-means for automatically taking .care of the Wide range ofcooling-rates which are necessary to Vtake care of the anode-cooling,under variable load-conditions. 1 v

yI- thus provide-*a small, ,compact vapor-discharge tube which hasnoexternal moving parts, either for artificially circulatingacooling-medium or for cooperating with thermally responsive devices. 1As previously intimated, however, my present Yinvention is notlimited,in its use, to the preferred construction which is shown in/Fig. l, asthefusible-material cooling-means is of generalbapplication to vanydevice having an internally heated partwhich is subject to a Wide vrangeof internal zheating, under-various operating-conditions of thejdevice.Inparticular, in vapor-electric; tubesgusin'g a discharge-metal ofcesium,-rubidium or potassium,` it is frequently desirable torapply my'fusible-material: coolingmeans lto the anode-portion of the evacuatedenclosure, Whether or. not said anode-portion constitutes acondensation-surface for the dischargemetal. My fusible-materialcooling-means is also-of, generalapplication to the maintenance vof thecondensation-temperature,.Within narrowly prescribed limits, regardlessof 4Whether the condensation-surface is a part of th'e anodeportion ofthe tube, orthe cathode-portion of the tube,` or some other separateportion of the tube. `j I have accordingly shown, in Fig. 3, analternative formof embodiment of my invention, in ayvapor-electric,device in `which the anode-portion 55 is held at such aternperature thatat least `apart of this anode portion 5'5 is the coolest part of thedevice, so as to .provide the condensationsurface. I'n Fig. 3,lthisanode-portion 55 is pro- Lvided with a fusible-material cooling-means65, having a ineltin'g-poiritat about the desiredcondensation-temperature.which controls the vaporpressure of the tube.The other parts`f'`the f .tubeVin Fig. 3, may bemore or less similar tothe construction which has `already been described .for Fig. l, exceptthat theproportions are dif- I claim'as my invention: j

1. A vapor-electric device having an evacuated enclosure-means includingan anode-portion of the enclosure-means, a cathode-portion of theenclosure-means, and an insulator-to-metal sealing-means between saidanode and cathode portions, a quantity of a discharge-metal selectedfrom the group comprising cesium, rubidium and potassium, aheating-means for heating the active emitting-portion of the cathode, acoolest-surface cooling-means for cooling some internal portionof thedevice to a temperature which is cooler than any other internal portionof the device during the operation of the device, whereby to provide acondensationsurface for the discharge-metalr and to control theoperating vapor-pressure of the dischargemetal, and anon-condensing-surface coolingmeans for cooling some other internal'portion of the device to a somewhat warmer temperature during theoperation of the device, whereby to prevent the condensation of saiddischarge-metal on said other internal portion; characterized by atleast one of said cooling-means including a fusible material having amelting-point at approximately the desired temperature to which saidcooling-means holds its associated internal portion of the device. n

2. The invention is defined in claim 1, characterized by saidfusible-material cooling-means comprising the combination; with anupstanding heat-conducting enclosure-portion of the device, adjacent tothe place which is to be internally cooled, of an upstandingheat-barrier spaced from the outer surface of said heat-conductingenclosure-portion, an upstanding heat-conducting cooling-plate spacedfrom the other side of said heat-barrier, said fusible material beingdisposed on both sides of said barrier and filling the space betweensaid heat-conducting enclosure-portion and said cooling-plate, and acontainer-means for said fusible material when it is melted, thedisposition and arrangement of the barrier and container-means beingsuch that molten fusible material can circulate over the top of thebarrier and under the bottom of the barrier.

3. A vapor-electric device having an evacuated enclosure-means includingan anode-portion of the enclosure-means, a cathode-portion of theenclosure-means, and an insulator-to-metal sealing-means between saidanode and cathode portions, a quantity of a discharge-metal selectedfrom the group comprising cesium, rubidium and potassium, aheating-means for heating the active emitting-portion of the cathode,and an anode-cooling means including a fusible material having amelting-point at approximately the desired temperature to which saidcooling-means holds said anode-portion of the enclosuremeans.

4. The invention as defined in claim 3, characterized by saidanode-cooling means comprising the combination, with an upstanding wallof said anode-portion, of an upstanding heatbarrier spaced from theouter surface of said upstanding wall, an upstanding heat-conductingcooling-plate spaced from the other side of said heat-barrier, saidfusible material being disposed on both sides of said barrier andfilling the space between said upstanding wall and said cooling-plate,and a container-means for said fusible material when it is melted,` thedisposition and arrangement of the barrier and containermeans being suchthat molten fusible material 8 can circulate over the top of the barrierand under the bottom of the barrier.

5. A vapor-electric device having an evacuated enclosure-means includingan anode-portion of the enclosure-means, a cathode-portion of theenclosure-means, and an insulator-to-metal sealing-means between saidanode and cathode portions, a quantity of a discharge-metal selectedfrom the group comprising cesium` rubidium and potassium, aheating-means for heating the active emitting-portion of the cathode, acoolest-surface cooling-means for cooling some internal portion of thedevice, other than said anode-portion, to a temperature which is coolerthan any other internal portion of the device during the operation ofthe device, whereby to provide a condensation-surface for thedischarge-metal and to control the operating vapor-pressure of thedischarge-metal, and a non-condensing-surface cooling-means for coolingsaid anode-portion to a somewhat warmer temperature during the operationof the device, whereby to prevent the condensation of saiddischarge-metal on said other internal portion; characterized by atleast one of said coolingmeans including a fusible material having amelting-point at approximately the desired temperature to which saidcooling-means holds its associated internal portion of the device.

6. The invention as dened in claim 5, characterized by saidfusible-material cooling-means comprising the combination, with anupstanding heat-radiating enclosure-portion of the device, adjacent tothe place which is to be internally cooled, of an upstandingheat-barrier spaced from the outer surface of said heat-conductingenclosure-portion, an upstanding heatconducting cooling-plate spacedfrom the other side of said heat-barrier, said fusible material beingdisposed on both sides of said barrier and filling the space betweensaid heat-conducting enclosure-portion and said cooling-plate, and acontainer-means for said fusible material when it is melted, thedisposition and arrangement of the barrier and container-means beingsuch that molten fusible material can circulate over the top of thebarrier and under the bottom of the barrier.

7. A vapor-electric device having an evacuated enclosure-means includingan anode-portion of the enclosure-means, a cathode-portion of theenclosure-means, and an insulator-to-metal sealing-means between saidanode and cathode portions, a quantity of a discharge-metal selectedfrom the group comprising cesium, rubidium and potassium, aheating-means for heating the active emitting-portion of the cathode,and a coolest-surface cooling-means for cooling said anodeportion to atemperature which is cooler than any other linternal portion of thedevice during the operation of the device, whereby to provide acondensation-surface for the discharge-metal and to control theoperating vapor-pressure of the discharge-metal; characterized by saidcooling-means including a fusible material having a melting-point atapproximately the desired temperature to which said cooling-means holdssaid anode-portion of the enclosure-means.

i8. The invention as defined in claim 7, characterized by saidanode-cooling means comprising the combination, with an upstanding wallof said anode-portion, of an upstanding heat-barrier spaced from theouter surface 4of said upstanding wall, an upstanding heat-conductingcoolingg plate spaced from the other side of said heatbarrier, saidfusible material being disposed on both sides of said barrier andfilling the space between said upstanding wall and said coolingplate,and a container-means for said fusible material when it is melted, thedisposition and arrangement of the barrier and container-means beingsuch that molten fusible material can circulate over the top of thebarrier and under the bottom of the barrier.

9. A vapor-electric device comprising an enclosure-means, an anode, acathode, and a quantity of a discharge-metal within said device, saiddischarge-metal being selected from the group consisting of cesium,rubidium and potassium; said cathode including a re-entrant metaltubeportion extending into said enclosure-means, said cathode-tubehaving a closed inner end, metal ns carried by said cathode-tube nearsaid closed inner end, a cathode-heater disposed within said cathodetube, said cathode-heater being concentrated at the finned end of thecathode-tube, and means for cooling the enclosure-entering end of thecathode-tube, said cathode-tube being long enough so that itsenclosure-entering end is the coolest part of the device, whereby thedischargemetal condenses thereon.

10. A vapor-electric device comprising an enclosure-means, ananode-portion of the en-A closure-means, a cathode, and a quantity of adischarge-metal within said device, said discharge-metal being selectedfrom the group consisting of cesium, rubidium and potassium; saidcathode including a re-entrant metal tube-portion extending into saidenclosure-means, said cathode-tube having a closed inner end, metal nscarried by said cathode-tube near said closed inner end, acathode-heater disposed within said cathode tube, said cathode-heaterbeing concentrated at the nned end of the cathode-tube, and means forcooling the enclosure-entering end of the cathode-tube, saidcathode-tube being long enough so that its enclosure-entering end is thecoolest part of the device, whereby the dischargemetal condensesthereon; and an anode-cooling means including a fusible material havinga melting-point at approximately the desired temperature to which saidcooling-means holds said anode-portion of the enclosing-means.

11. The invention as defined in claim 10, characterized by saidanode-cooling means comprising the combination, with an upstanding wallof said anode-portion, of an upstanding heat-barrier spaced from theouter surface of said upstanding wall, an upstanding heat-radiatingcooling-plate spaced from the other side of said heat-barrier, saidfusible material being disposed on both sides of said barrier andfilling the space between said upstanding wall and said cooling-plate,and a container-means for said fusible material when it is melted, thedisposition and arrangement of the barrier and container-means beingsuch that molten fusible material can circulate over the top of thebarrier and under the bottom of the barrier.

l2. A device having an internally heated part, an upstandingheat-radiating portion of the device for cooling said internally heatedpart, said heat-radiating portion having an upstanding outer surface, anupstanding heat-barrier spaced from the outer surface of saidheat-radiating portion, an upstanding heat-radiating coolingplate spacedfrom the other side of said heatbarrier, fusible material disposed onboth sides of said barrier and iilling the space between saidheat-radiating portion and said cooling-plate, and a container-means forsaid fusible material when it is melted, the disposition and arrangementof the barrier and container-means being such that molten fusiblematerial can circulate over the top of the barrier and under the bottomof the barrier, said fusible material having a melting-pointl atapproximately the desired temperature to which said heat-conductingportion is to be held.

13. A vapor-electric device comprising an enclosure-means, an anode, acathode, and a quantity of a discharge-metal within said device, saiddischarge-metal being selected from the group consisting of cesium,rubidium and potassium; said cathode including a metal tube-portionextending interiorly into said enclosure-means, a portion of saidcathode-tube carrying metal fins at a region within the interior of theenclosuremeans, means for heating the inside of the cathode-tube at theiinned portion thereof, and means for cooling the cathode-tube in aregion Where it enters the enclosure-means, said cathode-tube being longenough so that said cooled enclosureentering region is the coolest partof the device, whereby the discharge-metal condenses thereon.

14. A vapor-electric device comprising an enclosure-means, ananode-portion of the enclosure-means, a cathode, and a quantity of adischarge-metal within said device, said dischargemetal being selectedfrom the group consisting of cesium, rubidiurn and potassium; saidcathode including a metal tube-portion extending interiorly into saidenclosure-means, a portion of said cathode-tube carrying metal ns at aregion within the interior of the enclosure-means, means for heating theinside of the cathode-tube ai; the finned portion thereof, and means forcooling the cathode-tube in a region where it enters theenclosure-means, said cathode-tube being long enough so that said cooledenclosure-entering region is the coolest part of the device, whereby thedischarge-metal condenses thereon; and an anode-cooling means includinga fusible material having a melting-point at approximately the desiredtemperature to which said cooling-means holds said anode-portion of theenclosing-means.

l5- The invention as defined in claim 14, characterized by saidanode-cooling means comprising the combination, with an upstanding wallof said anode-portion, of an upstanding heatbarrier spaced from theouter surface of said upstanding wall, an upstanding heat-radiatingcooling-plate spaced from the other side of said heatbarrier, saidfusible material being disposed on both sides of said barrier andfilling the space between said upstanding wall and said coolingplate,and a container-means for said fusible material when it is melted, thedisposition and arrangement of the barrier and container-means beingsuch that molten fusible material can circulate over the top of thebarrier and under the bottom of the barrier.

JOHN L. BOYER.

No references cited.

